Conversion of hydrocarbons



l atented luly 26,. 1938 'No'lh'awing. Application October 15, 1936.80118] no. 105.111

PATENT OFFICE- REISSUEi-J 4. JUN 1940 Chicago. 111., a

4 (cl. zoo-.168)

' This invention relates particularly to the conversion of straightchain hydrocarbons into closed chain or cyclic hydrocarbons.

' More specifically, it is concerned with a process 5 involving the useof special catalysts and specific conditions of. operation in regard totemperature,

pressure and time of reaction whereby aliphatic hydrocarbons 'can beefliciently, converted into aromatic hydrocarbons.

' In the straight pyrolysis. of pure hydrocarbons or hydrocarbonmixtures such as those encountered in fractions from petrolemor othernaturally occurring or synthetically produced hydrocarbon mixtures thereactions involved which 15 produce aromatics from paraiiins and olefinsare of an exceedingly-complicated character and connot be very readilycontrolled.

It is generally recognized that, in the thermal decomposition ofhydrocarboncompounds or by- V 20 drocarbon mixtures of relatively narrowrange that whatever intermediate reactions are involved, there is anoverall loss of hydrogen, a tendency to carbon -separatlon'and agenerally wider boiling range in the total liquid products as comparedwith the original chargez. Under mild cracking conditions involvingrelatively low temperatures and pressures and short times of exposure tocracking conditions it is possible to there is a minimum loss ofhydrogen and a max imum production oi low. boiling fractions consistingof compounds representing the fragments of the original high molecularweight compounds.

.As the conditions of pyrolysis are increased in severity using highervtemperatures and higher times of exposureto 'pyrolytic' conditions,there olefins, naphthenes, aromatics, and finally into carbon andhydrogen and other light fixed gases.

It isnot intended to infer from this statement that any particularsuccess has attended the con- 55 version of any given parafiin or otheraliphatic some extent to control crackingreactions so that they arelimited to primary decompositions and.

these compounds are changed progressively into hydrocarbon into anaromatic hydrocarbon of the same number of carbon atoms by way of theprogressive steps shown. If this is done it is usually with very lowyields which are of very little or no practical significance. 5 Thesearch for catalysts to specifically control and accelerate desiredconversion reactions 'amonghydrocarbons has been attended with the usualdifficulties encountered in finding catalysts forv other types ofreactions since there are no 10 basic laws or rules for predicting theeffectiveness of catalytic materials and the a as a whole is in a moreor less empirical state. 11 using catalysts even in connection withconversion reactions among pure hydrocarbons and particularly in 15connection with theconversion of the relatively heavy distillates andresidua which are available for cracking, there is a general tendencyfor the decomposition reactions to proceed at a very rapid rate,necessitating the use of extremely short time factors and very accuratecontrol of temperature and pressure to avoid too extensivedecomposition. There are further difllculties encountered. inmaintaining the efiiciency of catalysts employed in pyrolysis sincethere is usually a rapid deposition of carbonaceous materials on theirsurfaces and in their pores. The foregoing brief review of the art ofhydrocarbon pyrolysis is given to furnish a general background forindicating the improvement .in such processes which is embodied in thepresent invention, which may be applied to the treatment of pureparaflin or olefin hydrocarbons, hydrocarbon mixtures containingsubstantial percentvages oi paraflln hydrocarbons such as relativelyclose cut fractions producible by distilling petroleum, and analogousfractions which contain unsaturated as well as saturated straight chainhydrocarbons, such fractions resulting from cracking operations upon theheavier fractions of pe- 4 troleum.

Inone specific embodiment the present inveution comprises the conversionof aliphatichydrocarbons including parafiin and olefin hydrocarbons intoaromatic hydrocarbons by subjecting them at elevated temperatures of theorder of 400-700 C. to contact for definite times of the order of 6-50seconds with catalytic materials comprising major proportions ofaluminum oxide of relatively low catalytic activity supporting minorproportions of oxides of elements selected from those occurring in thelefthand columns of" Group VI of the periodic table, these oxides havingrelatively high catalytic activity.

According to the 'present invention aliphatic or drogenation of thestraight chain hydrocarbons having 6 or more carbon atoms in chainarrangement in their structure are specifically dehydrogenated in such away that the chain of carbon atoms undergoes ring' closure with theproduction in the simplest case of benzene from n-hexane or n-hexene andin the case of higher molecular weight paraiiins of various alkylderivatives of benzene. Under properly controlled tact, temperature andpressure, very high yields of the order of 75 to 90% of the benzene oraromatic compounds are obtainable which are far in excess of anypreviously obtained in the art either with or without catalysts. For thesake of illustrating and exemplifying the types of hydrocarbonconversion reactions which are specifically accelerated underthepreferred conditions by the present types of catalysts, the followingstructural equations are introduced:

CH- CH: v on on 1: +411, CH1 CH: CH CH CH: CH

n-hexane benzene C-CH:

CH1 on on 0st. cal-on. on, on; on on on, v on n-heptane toluene on CH onC-CH;

CH: CHI-CH: :2 0 a v CHI-CH: CH C-CHs CH: C

n-octane o-xylene In the foregoing table the structural formulas.

conditions oftimes of con-" of the primary paraflln hydrocarbons havebeen represented as a nearly closed ring instead of by the usual lineararrangement for the sake of indicating the possible mechanisms involved.No attempt has been made to indicate the possible intermediate existenceof mono-olefinsf'dioleflns, hexamethylenes or "'alkylatedhexamethyienes' which"mightjresult from the loss of various amounts ofhydrogen. It present time whether ring closure occurs at the loss of onehydrogen molecule or whether dehychain carbons occurs so that the firstring compound formed is an aromatic such as benzene or one of itsderivatives. The above three equations are of a relatively simplecharacter indicating generally the type of reactions involved but in thecase of n-parafllns or mono-oleflns of higher molecular weight than theoctane shown and in the case of branched chain. compounds which containvarious alkyl substltuent groups indifferent positions along thesix-carbon atom chain, more complicated reactions will be involved. Forexample, in the case of such a primary compound as 2,3-dimethyl :hexanethe principal! resultant product is apparently o-xylene although thereare concurrentlyeflnite yields 'ofsuch compounds as produced ethylbenzene indicating an isomerization of two substituent methyl groups.'In the case of nonanes which are represented bythe compound;,3,4-trimethyl hexane, there is formation not'..

only of mesitylene'but also of such compounds as methyl ethyl benzol andvarious propyl benzols. i

is not known at the bons containing less elements chromium,

It will be seen from the foregoing that the scope of the presentinvention is preferably limited to the treatment of aliphatichydrocarbons which contain at least 6 carbon atoms in straight chainarrangement. In the case of paraflin hydrocarthan 6 carbon atoms inlinear arrangement, some formation of aromatics may take place due toprimary isomerization reactions although obviously the extent of thiswill vary considerably with the type of compound and the conditions ofoperation. The process is readily applicable to parafiins from hexane upto dodecane and: their corresponding oleflns. With increase in molecularweight beyond this point the percentage of undesirable side reactionstends to increase and yields of the desired alkylated aromatics decreasein proportion. 4

According to the present invention'composite catalytic materials areemployed which comprise in general major proportions by weight ofgranular activated aluminum oxide as a base catalyst or 4 supportingmaterial for minor proportions ofoxides of the elements in the lefthandcolumn of Group VI of 'the periodic table comprising the molybdenum, andtungsten. The base material comprising aluminum oxide is of relativelylow catalytic activity while the oxides of the elements mentioned are ofrelatively high catalytic activity and furnish by far the greaterproportion of the observed catalytic effects. The oxides of theseseveral elements vary somewhat in catalytic activity in any givenreaction comprised within the scope 'of the invention and this variationcase of different types of dehydrogenation and cyclization reactions.Some of. the properties of these catalytically active oxides, which aredeveloped on the surface and in the pores of the alumina particles willbe described in succeeding paragraphs.

It should be emphasized that in the field of may further vary in the. v

catalysis there have been very few rulesv evolved I which would enablethe prediction of what materials would catalyze a given reaction. Mostof the catalytic work has been done on a purely empirical basis, eventhough at times certain groups of" elements or compounds have been foundto be'more or less equivalent in acceleratingcertain types of reactions.Aluminum oxide which heat. Usually it is desirable and advantageous tofurther treat it with air or other gases, or by other means to'activ'ateit prior to use.

Two hydrated oxidesof aluminum occurin nature, to-wit:- bauxite havingthe formul'aAhOa.

21-120 and, diaspore A12Oa.H2O. In both of' these oxides ironsesqui-oxide may partially replace the alumina. These twominerals orcorresponding oxides produced from precipitated aluminum hye droxide areparticularly suitable, for the manufacture of the present type ofcatalysts and in some instances have given the best results of any ofthe base compounds whose .use is at present contemplated: The mineraldawsonite having the formula Na:Al(COa) 3.2A1(OH)3 is another mineralwhich may be used as a source'of aluminum oxide.

is generally preferable .as a base material for the manufacture of cata-I lysts for the process may be obtained from natural It is best practicein the final steps of preparing aluminum oxideas a base catalyst toignite it for some time at temperatures within the approximate range offrom 800-900 C. This probably does not correspond to completedehydration of the hydroxide but apparently gives a catalytic materialof good strength and porosity so that it is able to resist for a longperiod of time the deteriorating effects of the service and regenerationperiods to which it is subjected.

,My investigations have also definitely demon-- strated that thecatalytic efilciency of alumina, which has some catalytic potency initself. is greatly improved by the presence of oxides of the preferredelements in relativelyminor amounts, usually of the order of less than10% by weight of the carrier. It is most common practice to utilizecatalysts comprising 2 to 5% by weight of these oxides, particularly thelower oxides.

The oxides which constitute the principal active catalytic materials maybe deposited upon the surface and in the pores of the activated aluminagranules by' several alternate methods such as for example, the ignitionof nitrates which have been adsorbed or deposited from aqueous solutionby evaporation or by a similar ignition of precipitated hydroxides. Asan alternative method though 'obviouslyless preferable, the finelydivided oxides may be mixedmechanically with the alumina granules eitherin the wet or the dry condition. The pointoi achieving the most uniformpractical distrlbu-- tion of the oxides on the alumina should constantlybe borne in mind since the observed catalytic effects evidently dependprincipally upon a surface action.

The element chromium has three oxides, the trioxide CI'OQ, thedioxideCrO; and the sesquioxide OM03, the last-named being readily produced byheating the trioxide in hydrogen or hydrocarbon vapors at a temperatureof 250 ignition of the chromic acid, the nitrate or a C. The dioxide hasbeen considered to be an equimolecular mixture of the trioxide and the;sesquioxide. The oxides are readily developed on the surfaces and poresof alumina granules by utilizing primary solutions of chromic acidHaCrO; or chromium nitrate Cr(NO=) a. The

precipitated trihydroxide produces primarily the trioxide which is thenreduced to the sesquioxide to furnish an active catalyst for use inreactions of the present character.

The two most important oxides of molybdenum which are alternativelyemployed as catalysts ac'-. cording to the present invention are thedioxide M00: and sesquioxide M0203. Since the reduction of the trioxideby hydrogen begins at.300 C. (572 F.) and the reduction is rapid at 450C. (842 F1). the efiective catalytic material is principally thesesquioxide. The trioxide may be added-to the active alumina carrierfrom a solution in aqueous ammonia or from a solution .of ammoniummolybdate which are added in amounts just requisite to wet the carriergranules uniformly and the mass is then dried and ignited.

The' element tungstenhasthree oxides: the trioxide W03, the dioxideWOzand the sesquioxide W203. The trioxide. is readily soluble in aqueousammonia from which it may be deposited upon active alumina granules andit is ordinarily reduced preliminary to service by the action ofhydrogen at a red heat. Tungstic acids may be precipitated from aqueoussolution to form the hydrated oxides and these may be desiredcyclization reactions with tillates willbe increased and of oxides onthe carrier particles.

3 heated to drive off water and leave a In regard to uranium,,which isthe heaviestmember of the present natural group of elements-- whoseoxides are preferred as catalysts, it may merely be statedthat whilethis element furnishes catalytic oxides having some order of catalyticactivity, its scarcity and cost naturally pres,

cludes its extensive use in practice,

' It has been found essential to. the production of high yields ofaromaticsfrom aliphatic. hy-

drocarbons when using the preferredtypes of catalysts-that dependingupon the aliphatic hydrocarbon or mixture of treated, temperatures frombe employed. contact times to 50 seconds and pressures 400 l00 0. shouldof approximately 6 approximating athydrocarbons eing mospherie, The useof subatmospheric pressures of the order of V atmosphere may bebeneficial in that reduced pressures generally favor selectivedehydrogenation reactions but on the other hand moderatelysupe'ratmospheric pressures usually of the order of less than lbs. persquare inch tend to increase the capacity ofcommercial plant equipmentso that inpractice a balance is struck between these two factors. Thetimes of contact most commonly employed with n-parafilnic ormono-olefinic hydrocarbons having from 6-12 carbon atoms tothe moleculeare of the'order of 8-20 seconds. It will be appreciated by thosefamiliarwlth the art of hydrocar-' bon conversion in the presence ofcatalysts that the factors of temperature, pressure and .time

, will frequently have to be adjusted from theresults of preliminaryexperiments to produce the best results in any given instance. Thecriterion,

of the yield of aromatics will serve to'fix the best conditions ofoperation. In ageneral sense the relations between time, temperature andpressure are preferably. adjusted so that rather intensive conditionsare employed of sufll'cient severity to insure a maximum amount of the aminimum of undesirable side reactions. If too short times of contact areemployed the conversion reactions 'will not proceed beyond those ofsimple dehydrogenation and the. yi l s of oleflns and diolefins willpredominate over those of aromatics.

While the present process is particularly applicable to the productionof the corresponding aromatics froman aliphatic hydrocarbon or a mixtureof aliphatic hydrocarbons, the invention may also be employed to producearomaticsfrom aliphatic hydrocarbon mixtures such as'distillates fromparafl'inic or mixed base crude petroleum. In this case the aromaticcharacter of the disas a rule the octane number will be higher. feasibleon a basis of concentration, the aromatics produced in' the hydrocarbonmixtures may be recovered as such by' distillation into fractions -ofproper boiling range followed by chemical treatment with reagentscapable of reacting selectively with them. Another method of aromaticconcentration willinvoive the use of selective solvents such as liquidsulfur dioxide, alcohols, furfural, chlorex, etc;

In operating the process the general procedure is to. vaporizehydrocarbons or drocarbons and after heating the, vapors to a suitabletemperature within the ranges previously specified, to pass themthrough'stationary masses of granular :catalytic materialinverticalcylindricah treating columns 0 banks of catalystcontaining tubes inparallel connection. Since mixtures of hy-.

If desired and found i the reactions vare endothermic it with theseparation of.

may be necessary to apply some heat externally to maintain the bestreaction temperature. After passing through the catalytic zonetheproducts are submitted to fractionation to recover cuts or fractionscontaining the desired aromatic product hydrocarbons and heavierresidual materials,

which may be disposed of in any suitable manner.

depending upon their composition. The overall yield of aromatics may beincreased by recycling the unconverted straight chain hydrocarbons tofurther treatment with this is a more or less obvious expedient and notspecifically characteristic of the/present invention.

It is an important feature of the present procof the reasons for thedeleterious influence of water vapor on the course of the present typeof catalyzed reactions, but it may be suggested that the action ofthesteam may be to cause a partial hydration of alumina and some of thecatalytic oxides due to preferential adsorption so that in effect thehydrocarbons are prevented from reaching or being adsorbed by thecatalytically active surface The present types of catalysts areparticularly effective in removing hydrogen from chain compounds in sucha way that cyclization may be promoted without removal of hydrogen fromend carbon atoms so that both end and side alkyl groups may appear assubstituents in benzene rings and it has been found that under properoperating conditions they do not tendto promote any great amount ofundesirable side reactions leading to' the'deposition of carbonorcarbonagas at a moderately elevated ceous materials and for this reasonshow reactivity over relatively long periods of time. When theiractivity begins to diminish after a period of service, it is readilyregenerated by the simple expedient of oxidizingwith air or otheroxidizing temperature, usually within the range employed in thedehydrogena- This oxidation effectively removes traces of carbondeposits which contaminate the surface of the particles and decreasetheir efliciency. It is characteristic of the present types of catalyststhat they may be repeatedly regenerated with only a very gradual loss ofcatalytic efficiency.

During oxidation with air or other oxidizing gas mixture in regeneratingpartly spent mate rial, there is evidence to indicate that the loweroxides are to a large extent, if not completely,

- oxidized to higher oxides which combine with aluminum oxide to formaluminum salts of variable composition. Later. these salts are decomposed by contact with reducing gases in the first stages of service toreform the loweroxides and regenerate the real catalyst and hencethecata-' lytic activity.

' Example I In this example an ultimate yield of over 90% benzol wasproduced by the catalytic conversion ,of an n-hexane. fractionobtained-from a highly parafiln ic crude petroleum by closefractionation. The catalyst comprised ing about 4% by weight of chromiumsesquioxide fixed gases, unconverted fresh material, although an aluminabase supportwhich had been developed on the carrier particles I by theignition of chromium nitrate and the reduction of the primary trioxideby hydrogen at a temperature of 250-3G0 C. The hexane fraction waspassed through a bed of this cat'al'ystat a temperature of 525 C.,atmospheric pressure and a time of contact of 20 seconds to produce aonce-through yield -of about 47%. The final yield after recyclingunconverted-hexane several times was above 90% as previously stated.

Example '11 f In this case n-heptane was converted to toluene utilizinga catalyst supporting molybdenumpx ides on the preferred alumina base.The catalyst was made by utilizing a solution of ammonium" molybdate inan excess of ammonia and adding the concentrated solution to about threetimes its weight of granular alumina particles followed by carefulmixing and calcining to drive ofl water and ammonia and leave a residueof the trioxide. Before service the particles were treated with hydrogenat about 450 C. to reduce a material portion of the trioxide tolower'oxides such as the sesquioxide.

, n-I-Ieptane.was passed over a'bed of the catalyst particles at atemperature of 555v C'., atmospheric pressure and 13 seconds contacttime to produce a yield of approximately 50% of toluene on aonce-through basis, this yield being finally raised to about 80% bycomplete recycling of unconverted material.

Example III Example 1V To prepare thecatalyst an ammonlacal aque oussolution of tungsten trioxide was used to 'deposit the trioxide upon anactivated alumina. After reduction with hydrogen, analyses showed therewas present from 4-5% of mixed tungsten oxides.

Using the tane were treated at a temperature of 560 0.,

substantially atmospheric pressure, and 15 seg onds contact time toproduce a yield of 46%' of toluene on a once throughbasi's which wasfinally brought to'about a 16% ultimate yield after several recyclingsof unconverted charge.

The foregoing specification and examples show clearly the character ofthe invention and the res'ults'to be expected in its application toallphatic. hydrocarbons, -although neither section is intended to beunduly limiting.

I claim as-my invention:

l. A process for the production of aromatic \hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the aliphatic hydrocarbonbyssubjectionto a temperature of the order of 400 to 700 column of Group'VI' of -the periodic table and C. for a period of about 6 to 50seconds, in the presence of an aluminum 7 a selected from the classconsisting. of chromium,

molybdenum, tungsten and uranium.

, 1 50 above catalystthevapors of n-hep- 2. A-process for the productionof aromatic hydrocarbons from aliphatic hydrocarbons of from six totwelve carbon atoms, which c0mprises dehydrogenating and cyclicizingtheoaliphatic hydrocarbon by subjection to a temperature of the order of400 to 700 C. for a period oi. about 6 to 50 seconds, in the presence ofan aluminum oxide catalyst containing a relatively small amount of anoxide oi. chromium.

3. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to. twelve carbon atoms, which comprisesdehydrogenating and cyclicizlng the aliphatic hydrocarbon by subjectionto a temperature otthe order 01' 400 to 700 C. for a period'o! about 6to 50 seconds, in the presence 0! an aluminum oxide catalyst containinga relatively small amount of an oxide of molydenum.

4. A process for the production of aromatic hydrocarbons irom aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdefhydrogenating and cyclicizing the aliphatic hydrocarbon by subjectiontd a temperature of the order ot400 to Z00 C. for a period or about 6 to50 seconds, in the presence of an aluminum oxide catalyst containing arelatively small amount of an oxide of tungsten.

- ARISTID V. GROSSE,

